The present invention relates to a biosensor for facilitating rapid quantitation of a specific component contained in a biological sample with high accuracy.
So far, various biosensors have been developed as a system for facilitating simple quantitation of a specific component contained in a sample, without necessitating dilution or agitation of a sample solution.
Biosensors utilizing enzyme reaction use a carrier that carries or contains an enzyme reaction system. These biosensors use light, color, or electrical signal as a means for signal transmission.
An example of the biosensor utilizing the electrical signal as a signal transmitter is disclosed in Japanese Laid-Open Patent Publication Hei 3-202764, wherein an electrode system comprised of a working electrode and a counter electrode is formed on an electrically insulating base plate by screen printing or the like, followed by formation of an electrically insulating layer thereon, then an enzyme reaction layer containing a hydrophilic polymer, an oxidoreductase, and an electron acceptor is formed over the above-mentioned electrode system. Addition of drops of a sample solution containing a substrate as a measuring substance on the enzyme reaction layer causes dissolution of the enzyme reaction layer. As a result, reaction between the substrate and the enzyme proceeds, and the substrate is oxidized, which in turn promotes reduction of the electron acceptor. At completion of the enzyme reaction, the reduced electron acceptor is electrochemically oxidized, and a current level for oxidation measured at that time is used to determine the concentration of the substrate contained in the sample solution.
The biosensor having the above-described conventional structure, however, has a drawback that a response of the biosensor may vary by the presence of any components contained in the sample solution other than the substrate, even when the sample solution contains the substrate at an equal concentration. Taking an example, the presence of a substance in the sample solution which affects pH value often causes a change in enzyme activity, thereby varying the response of the biosensor. In the case of blood sample that contains particle components such as red blood cells, for example, a difference in the concentration of such particle components causes a difference in the sensor response.
An effective method to relieve the difference in the nature of the sample solution is to decrease this difference by diluting the sample solution using a dilute solution. However, this method is not necessarily advantageous from the aspect of ease of operation.